1. Field of the Invention
The present invention is generally in the field of semiconductors. More specifically, the present invention is in the field of fabrication of transistors.
2. Background Art
Power semiconductor devices, such as field-effect transistors (FETs) are widely used in a variety of electronic devices and systems. Examples of such electronic devices and systems are power converters, such as DC to DC converters, in which vertically conducting trench type silicon FETs, for instance, may be implemented as power switches. In power converters, power losses within the power switches, as well as factors affecting switching speed, are becoming increasingly important. For example, for optimal performance it is desirable to reduce overall gate charge Qg, gate resistance Rg, and ON-resistance Rdson of the power switches.
Optimizing Rdson in a vertical trench FET, for example, may require carefully controlling the length of the channel. That is to say, implementation of a vertical trench FET having a short channel may improve the Rdson characteristic of the device. However, conventional methods of forming vertical trench FETs can undesirably affect channel length rendering a short channel unachievable and the channel length uncontrollable. For example, conventional methods can expose dopants, used to form the channel, to high temperature processes, thereby uncontrollably increasing channel length. Moreover, the conventional vertical trench FET requires deep trenches to, for example, counter the lack of control over the channel length.
Thus, there is a need for a method that can provide trench FETs while overcoming the drawbacks and deficiencies in the art.